I'd be against the idea if I were the DM of the game. The pact is delicious RP gold. The sacrifice of the character is part of the problems the character must overcome, or revel in. Having the bill paid by someone else feels like it would detract from that.

Edited: obviously the obligatory "you do you" must go here. If you and your DM are happy with it then go with it.

not really fluff, considering that can change whether the fiend could tell you to just murder your party in their sleep or not, i know the dm wouldn't have that (unless you and them decided to come together for a character arc for your character, or the dm just shitty) but it would actually make a difference, well, if they were a devil atleast, a demon doesn't give a shit what the contract says

That's really... Lame. Part of being a Warlock I'd that you're tied to a powerful being. If you write it off that someone else made the pact for you, you're just dodging the whole allegiance you have to the demon.

I would argue that the warlock would still have to fulfill the pact or feel a compulsion to do so, but would wrestle with their own personal feelings about it. Instead of a willing servant to this fiend, they were offered up, and they have no way out. that could be spun into a good rp, too, given enough thought.